(1) Field of the Invention
The present invention relates to an image forming apparatus which forms images on a recording medium by causing a developer to jump thereto. It may be used for a printer unit in digital copiers and facsimile machines as well as for digital printers, plotters, and the like.
(2) Description of the Related Art
Recently, as the image forming means for outputting a visual image on recording medium such as paper etc., in response to an image signal, an image forming apparatus has been disclosed in Japanese Patent Application Laid-Open Hei 5 No. 134,581, for example, wherein charged particles are placed in an electric field so that they will jump by electric force to adhere to the recording medium whilst the potential to be applied to the control electrode having a number of passage holes located in the jump passage is being varied, to thereby form an image on the recording medium, directly.
In the above-mentioned related art, a method of controlling the developer is described, but the method suffers from many problems as shown below.
An image forming apparatus of a type of the above related art uses a control means for controlling the passage of charged particles through the gates. In the image forming apparatus of the type of the conventional art, jumping of the toner (developer), either the release or prohibition of the jumping, is controlled by regulating the electric field generated between the gates and the toner support while the strong electric field produced by the opposing electrode causes the toner to transfer to the surface of a paper as a recording medium and form an image thereon.
In the above-mentioned image forming apparatus, no charge having a polarity opposite to that of the toner will be given to the rearside of the recording medium, unlike the transfer process in the Carlson process. Therefore, when the recording medium slides on the metal disposed in its conveyance path, the charge on the toner constituting the image induces a very strong image force with respect to the metal. In this situation, a force acts on the toner on the recording medium in the direction opposite to the direction of movement of the recording medium, especially at the end portion of the metal. This causes the toner on the recording medium to move relatively from each other and form an image with a rubbed-like appearance, resulting in a disturbed developed image.
Further, in the image forming apparatus using plural colors of toner, this type of disturbance in the image causes color mixing of the multiple colors of toner, producing a new problem, that is, a failure in correct color reproduction.